[Hallicrafters] SX 101A hum: how much is too much?

[Glen Zook]

Obviously you are using "modern" stereo headphones! 
The old high impedance (usually around 2000 ohm
impedance) do not reproduce the very low frequencies
that the stereo headphones reproduce.  Thus, when the
receiver was new, virtually no one was trying to use
stereo headphones and no one could hear the "hum".

Yes, I can hear some "hum" on all of my tube type
receivers if I use stereo headphones and not the high
impedance types.  Frankly, it is pretty much a "fact
of life" when using the new type low impedance
headphones.  Some receivers are worse than others,
but, generally, you are going to hear some "hum". 

Now, don't replace the tubes in the receiver just to
replace the tubes!  Tubes last for decades.  All that
you usually do when you replace all of the tubes is
make it necessary to realign the receiver.  Also, as
the tubes "age", the alignment is going to "drift"
somewhat as well.  The tubes that are in the receiver
are fine so long as it meets specifications.  In fact,
sometimes, putting in newer tubes can cause problems
like oscillations because of higher gain, especially
when more than one tube is replaced.

It is fine to have a replacement set of tubes for your
equipment.  That is if, and when, a tube finally goes
bad that you can replace it.  Of all the equipment
that I have worked on for others, only one Collins
75A2 receiver has ever required more than a total of 3
tubes to get it working properly!  That particular
receiver required 9 tubes, but it definitely has been
the exception!

Glen, K9STH

 
--- Andy Bullington <abullington at comcast.net> wrote:

I got a mono adapter for my headphones and noticed
....hum!! At all or no volume level, all or no rf
level...doesn't seem to make a difference.

I'm waiting on a shipment of NOS tubes but something
tells me thats not the problem. Or is this just a fact
of life with old tube receivers? 

=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

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